Among known substrates that include electrically conducting elements are window panes, widely used in the automotive field. The electrically conducting elements are usually employed as heating tracks, especially on rear windows, but they may also be placed on a window pane in order to provide an alarm and/or an antenna function thereat.
In practice, the electrically conducting elements consist of metal wires that are formed on an industrial scale by conventional screen-printing of an electrically conducting paste, forming a predetermined pattern, and by firing this paste.
The pattern gives the elements a precise width and a precise thickness depending on the final function of said elements, for example in relation to the desired impedance of an antenna.
Owing to the useful functions (heating, antenna, alarm) provided by these conducting elements, their number on a given window pane has been increasing in recent years, which can pose space constraint and visibility problems. Thus, when the tracks are located in the field of view of the window pane, they are clearly visible from the inside, which may impede the driver, and possibly from the outside, which impairs the aesthetics of the vehicle.
Thus, for a few years now, conducting elements have instead been produced in the form of transparent metal films that are etched or cut into the desired pattern.
Moreover, although several years ago an antenna was dedicated only to receiving radio waves, the growing technology in the telecommunications field is increasingly dictating the provision of antennas endowed with various types of transmission and/or reception characteristics, such as GPS, mobile telephony, etc.
Thus, a vehicle is presently provided with conventional receive antennas, such as conducting wires placed on the rear windows, and with more specific antennas, such as for GPS systems, mobile telephony systems, telepayment systems, etc., which consist of wire antennas or antennas configured in the form of patches and placed for example on the roof of the vehicle, or which consist of transparent conducting films deposited on the window panes.
Since all these applications do not operate at the same frequency, it is necessary to configure a specific antenna for each application. This does not simplify the manufacture of a vehicle and represents additional production and vehicle incorporation costs.
A new type of antenna has recently appeared on the market, called a fractal antenna, which makes it possible with a single device to operate over one or more frequency bands and which also is miniaturized.
A fractal antenna has a pattern with a fractal geometry, that is to say a base pattern that is repeated several times, possibly on a different and homothetic size scale, so as to cover one or more frequency bands.
U.S. Pat. No. 6,300,914 for example describes a fractal antenna in the form of a loop that is 5 to 10 times smaller than an equivalent low-frequency conventional antenna. This antenna is for example formed by a conducting film deposited on a substrate and cut to the desired shape.
Various shapes of antennas having a fractal geometry may be envisaged. Patent application WO 02/01668 thus discloses various patterns, such as triangular, Hilbert curve, Von Koch snowflake and Sierpinski carpet patterns, or a combination of these patterns, the antennas being obtained from conducting films formed on substrates.
These fractal antennas formed by transparent films may also be incorporated into window panes by being deposited on supports, for example flexible plastic films, which are then laminated between two substrates to form the window pane. Document U.S. Pat. No. 6,552,690 shows this type of window pane. However, such a manufacturing process remains complicated to implement.
Such antennas formed on rigid supports, such as plastic supports, but incorporated into rearview mirror assemblies, thus eliminating from view the conventional antennas placed on the roof, are also known.